Experimental study on the compressive strength, damping and interfacial transition zone properties of modified recycled aggregate concrete

© 2019 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. At present, many modification methods have been proposed to improve the performance of recycled aggregate concrete (RAC). In this study, tests on the compressive strength and damping properties of modified RAC with the addition of different proportions of recycled coarse aggregate (RCA) (0, 50, 100%), rubber powder (10, 15, 20%), steel fibre (5, 7.5, 10%) and fly ash (15, 20, 5%) are carried out. To elucidate the effect of the modification method on the interfacial transition zone (ITZ) performance of RAC, model ITZ specimens are used for push-out tests. The results show that when the replacement rate of RCA reaches 100%, the loss factor of the RAC is 6.0% higher than that of natural aggregate concrete; however, the compressive strength of the RAC decreases by 22.6%. With the addition of 20% rubber powder, the damping capacity of the modified RAC increases by 213.7%, while the compressive strength of the modified RAC decreases by 47.5%. However, with the addition of steel fibre and fly ash, both the compressive strength and loss factor of the RAC specimens increase. With a steel fibre content of 10 wt%, the compressive strength and loss factor of the RAC increase by 21.9% and 15.2%, respectively. With a fly ash content of 25 wt%, the compressive strength and loss factor of the RAC increase by 8.6% and 6.9%, respectively. This demonstrates that steel fibre and fly ash are effective in improving both the damping properties and compressive strength of RAC, and steel fibre is more effective than fly ash. Two methods were used for modification of the RAC: reinforcing the RCA through impregnation with a 0.5% polyvinyl alcohol (PVA) emulsion and nano-SiO2 solution, and strengthening the RAC integrally through the addition of fly ash as an admixture. Both of these techniques can improve the ITZ bond strength between the RAC and new mortar. Replacing 10% of the cement with fly ash in the new mortar is shown to be the best method to improve the ITZ strength

Numerical Simulation of a Latent Heat Storage System of a Solar-Aided Ground Source Heat Pump

In this study, the rectangular phase change storage tank (PCST) linked to a solar-aided ground source heat pump (SAGSHP) system is investigated experimentally and theoretically. The container of the phase change material (PCM) is the controlling unit of the phase change heat transfer model. It was solved numerically by an enthalpy-based finite difference method and was validated by experimental data. CaCl2•6H2O was used as the PCM in the latent heat storage system of SAGSHP system. In the tank, the PCMs are encapsulated in plastic kegs that are setting on the serpentine coil. The experiments were performed from March 12 to April 10, 2004 in the heating season of the transition period. In order to reflect the effects of the system, two days were chosen to compare the numerical results with experimental data. The inlet and outlet temperature of the water in the PCST, temperature of PCM and storage and emission heat of PCST were measured. The trends of the variation of numerical results and experimental data were in close agreement. Numerical results can reflect the operation mode of the system very well

η\eta-meson in nuclear matter

The $\eta$-nucleon ($\eta$N) interactions are deduced from the heavy baryon chiral perturbation theory up to the next-to-leading-order terms. Combining the relativistic mean-field theory for nucleon system, we have studied the in-medium properties of $\eta$-meson. We find that all the elastic scattering $\eta$N interactions come from the next-to-leading-order terms. The $\eta$N sigma term is found to be about 280$\pm$130 MeV. The off-shell terms are also important to the in-medium properties of $\eta$-meson. On application of the latest determination of the $\eta$N scattering length, the ratio of $\eta$-meson effective mass to its vacuum value is near $0.84\pm0.015$, while the optical potential is about $-(83\pm5)$ MeV, at the normal nuclear density.Comment: 8 pages, 3 figures, to appear in PRC, many modification